Essentially, a dual-clutch transmission has two trains or sub-transmissions, as the case may be, with different pairs of gear wheels, two power-shifting clutches, each of which is allocated to a sub-transmission, one drive shaft and one output shaft, along with, depending on the number of gears, positive-locking, non-synchronized shifting clutches. Thereby, the gears are arranged on an alternating basis in the two sub-transmissions, such that it is possible to pre-select a gear in the load-free sub-transmission, while the torque is transferred from the other sub-transmission. A gear shift is realized by the torque to be transferred being delivered from one power-shifting clutch to the other power-shifting clutch, such that the gears can be shifted without load and without any interruption of the pulling force, and without a tensioning of the shiftable gears. As a rule, with one sub-transmission, the odd gears can be shifted and, with the other sub-transmission, the even gears and the reverse gear can be shifted.
Parking lock mechanisms for automatic transmissions, particularly for dual-clutch transmissions, are known in the state of the art. Typically, such mechanisms feature a preloaded spring, through which the parking lock is activated, whereas the parking lock function is realized by a locking pawl/rack system. For deactivating the parking lock, a mechanical gear rod or a hydraulically or pneumatically actuated piston is typically used. In doing so, an actuating rod of a gear rod, or a piston rod of the piston, as the case may be, which for its part is arranged in an axially displaceable manner in a piston bore of the actuator housing, works together with a parking lock pawl and a parking lock gear.
The locking element of such a parking lock mechanism, which is usually formed as a locking pawl, is, in the locked state, typically clamped between a parking lock pawl and a guide plate, in order to prevent the parking lock pawl from being pushed out of the gap in the teeth of a parking interlock gear connected to the output of the transmission.
Upon engaging the parking lock, the parking lock pawl is pressed by the locking pawl into the toothing of the parking interlock gear, and is thereby supported against the guide plate, whereas, with an engaged parking lock, a torque applying at the transmission by the drive wheels on the output side is supported by the ratchet. Such torque may be generated in particular by the fact that the road inclination is great, that is, the vehicle is in the forward direction of uphill or downhill, and the downhill force thereby acting on the vehicle on the output side is introduced into the drive train, by which the drive train is preloaded between the drive wheels and the parking lock.
Upon the disengagement of the parking lock, the locking pawl is displaced in the axial direction, by which the parking lock pawl under tension as a result of the tensioning of the drive train is released as part of a sudden relaxation. During this process, a release jolt disadvantageously occurs, since the parking lock pawl is moved very rapidly in the direction of the locking pawl and the guide plate and, with its end turned away from the parking lock pins, strikes on the guide plate, by which an undesired and loud metallic noise is generated. This sound continues to propagate as a structure-borne sound through the components located in the power flow with the ratchet, up to the transmission housing, and from there is radiated outwards as a sound, which is also perceived as an unpleasant shock.
A device for damping torsional vibrations upon disengaging a parking lock is known from DE 10 2008 000 177 A1 of the applicant, whereas the parking lock features a parking interlock gear connected to the output of the transmission, a ratchet swivel-mounted by a parking lock pin in a transmission housing, which is engaged or disengaged in the parking interlock gear and the swiveling end of which is guided into a guide plate connected to the transmission housing, and a locking element that, in the locked state, is clamped between the ratchet and the guide plate, in order to prevent the pushing out of the ratchet from a gap in the teeth of the parking interlock gear. The known device features a rotatably mounted latch with a latch tooth that is engageable in the toothing of the parking interlock gear, which is connected to an axially acting damping device for tensile and compressive loads, and is arranged in such a manner that, upon the engagement of the parking lock against the force of a return spring, it is pressed in a positive-locking manner into the toothing of the parking interlock gear, whereas, upon the disengagement of the parking lock, a rotational movement of the parking interlock gear of the latch tooth of the latch that meshes in a positive-locking manner in the parking interlock gear is braked or damped, both upon forward and reverse movement, due to the damping effect of the damping device.